1. Field
Aspects of the present disclosure relate to negative electrodes, negative active materials, methods of preparing the negative electrodes, and lithium batteries including the negative electrodes, and more particularly, to negative electrodes with high charge and discharge efficiency and good cycle characteristics, negative active materials, methods of preparing the negative electrodes, and lithium batteries including the negative electrodes.
2. Description of the Related Art
Lithium batteries are rechargeable at high rates, and have an energy density per unit three times greater than those of conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, etc. Since lithium batteries operate at high operating voltages, they are not used together with an aqueous electrolyte solution that is highly reactive to lithium. In general, lithium batteries include an organic electrolyte solution. The organic electrolyte solution is prepared by dissolving a lithium salt in an organic solvent. An organic solvent that is suitable for preparing the organic electrolyte solution may be any one of various solvents that are stable at high voltage and have high ion conductivity, a high dielectric rate, and low viscosity.
If a lithium battery includes a polar carbonate-based and non-aqueous solvent, excess charges are used due to a side reaction between a carbon electrode that is a negative electrode and an electrolyte solution during initial charging, which is an irreversible reaction. Due to the irreversible reaction, a passivation layer such as a solid electrolyte interface (SEI) is formed on the surface of the negative electrode.
During charging and discharging, the SEI prevents decomposition of the electrolyte solution and performs as an ion tunnel. During charging and discharging, the SEI allows only lithium ions to pass therethrough, and blocks flow of the organic solvent moving together with lithium ions in the electrolyte solution.
Only lithium ions are intercalated in the carbon electrode that is a negative electrode and the organic solvent is not cointercalated with the lithium ions, thereby preventing collapsing of the structure of the negative electrode. In general, an additive, such as vinylene carbonate or vinylene sulfate, is used in an electrolyte solution of a lithium battery in order to form a high-quality SEI on the surface of the negative electrode, and the use of the additives leads to higher capacity retention rate, better cycle characteristics, and higher stability of the lithium battery.
However, the greater surface area of the carbon electrode that is a negative electrode and the smaller carbon particle size, for example, a nanoparticle size, bring about more side reactions between the carbon electrode that is a negative electrode and the electrolyte solution and thus, the SEI is not formed. Thus, high capacity retention rate and good cycle characteristics of a lithium battery may not be obtained only by using the additives of the lithium battery.